In the liquid-level detection devices applied to automatic clinical analyzers, it has become common that a configuration having a liquid-level detection function added to a dispensing probe is employed to respond to a call for further improvement of measured-data accuracy. A recently known type of probe provided with a liquid-level detection function utilizes capacitance to use the probe itself as an electrode for liquid level detection.
The capacitive type detects the liquid level of a liquid sample by measuring a very insignificant variation in capacitance between the dispensing probe and the sample accommodated in a container, and utilizing the characteristic that contact of the probe with the surface of the liquid sample increases the variation in capacitance.
In the capacitive type, it is necessary that the variation in capacitance of the liquid sample be converted into an electrical signal variation. The bridge circuit schemes disclosed in JP-A-62-218818 and JP-A-63-259420 are known as recent examples of methods of the conversion. These conventional bridge circuit schemes including a bridge circuit to form, as part of the device components, an element having very small capacitance between a dispensing probe and a liquid sample, convert a variation in the capacitance into an output signal variation of the bridge circuit.
The differential circuit scheme disclosed in JP-A-02-59619 is known as a further example. In this conventional circuit scheme, a differential circuit is provided that differentiates a reference signal in accordance with the very small capacitance developed between a dispensing probe and a liquid sample, and a variation in the capacitance is converted into an output signal variation of the differential circuit.
In the capacitive schemes discussed above, the very small capacitance between the dispensing probe and the liquid sample needs to be measured accurately. In addition, reagent containers are mounted on a reagent disk. In the discussed schemes, however, oscillation of the liquid surface due to reagent disk rotation during liquid level detection has occasionally caused errors in detection results.
The reagent container disclosed in JP-A-2000-275251 is known as an example of a container constructed so as to suppress the oscillation of the liquid surface of a reagent as discussed above. This conventional reagent container is used in an automated analyzer that employs, for example, a rotary table or any other suitable transport means to transport the reagent container to a predetermined position at which the reagent that is the internal contents of the container is to be dispensed by probes or suction nozzles. The reagent container is constructed so as to suppress the oscillation of the liquid surface due to centrifugal force upon the container-accommodated reagent during the transport of the container, by generating fluid resistance in a centrifugal direction over a vertical range including a height region corresponding to an accommodation zone of the liquid, between a centrifugal proximal section of the smallest centrifugal force and a centrifugal distal section of the largest centrifugal force.
Japanese Patent Publication No. 3845305 proposes a reagent container as another example of a container constructed so as to suppress the oscillation of the liquid surface of a reagent, this reagent container being responsive to the oscillation occurring when the container is moved linearly by a belt conveyor or other means.